The following relates to the electrical arts, electrical device arts, electromagnet arts, electric motor arts, nuclear reactor arts, and related arts.
A pressurized water reactor (PWR) employs a pressure vessel containing superheated water as the primary coolant. Hot, subcooled water is circulated between the reactor core and one or more steam generators to transfer energy from the reactor core to the steam generator. In a conventional design, the steam generators are separate elements and the primary coolant is coupled between the pressure vessel and the steam generator via suitable high pressure fluid conduits. In an integral PWR design, the one or more steam generators are located inside the pressure vessel. Other types of nuclear reactors are similar. For example, a boiling water reactor (BWR) employs boiling primary coolant which is not superheated.
It is advantageous to include motorized components inside the pressure vessel of a nuclear reactor. For example, in some reactor designs the primary coolant is actively circulated using electric motor-driven coolant pumps. The pumps may be located outside the pressure vessel and mechanically coupled with the impeller via a rotating shaft passing through a suitable vessel penetration. However, it is advantageous to eliminate the mechanical pass-through vessel penetration by employing wholly internal motor-driven coolant pumps. In this latter design, only small and mechanically static vessel penetrations for electrical cabling are employed.
Another place where a motorized component can be useful is in control rod drive mechanism (CRDM) components. A control rod containing a neutron absorber is inserted partway or fully into the reactor core in order to moderate or stop the nuclear reaction. In so-called “gray” rods, the extent of the rod insertion is adjustable in a continuous or step-wise fashion in order to provide adjustable reactivity control. Traditionally, the electric motor operating the control rod is located outside the pressure vessel (typically above the pressure vessel in PWR designs or below the pressure vessel in BWR designs) and a connecting rod passes through a suitable vessel penetration to connect the CRDM motor with the control rod. Again, it is advantageous to eliminate the mechanical vessel penetration by employing a wholly internal CRDM in which the electric motor operating the control rod is located inside the pressure vessel, so that only mechanically static vessel penetrations for electrical cabling are employed.
Employing electric motors inside the pressure vessel is complicated by the high temperature of the primary coolant. The electric motor and its constituent materials must be robust against the high temperature of the reactor environment, and must also be robust against other environmental conditions such as corrosive chemicals and/or radioactivity that may be present in the primary coolant. For example, PWR reactors typically employ boric acid as a soluble reactivity-moderating neutron poison in the primary coolant. Moreover, the electric motor must be reliable since any maintenance entails the costly proposition of shutting down and opening the reactor while taking suitable containment and radioactive waste control precautions.
Disclosed herein are improvements that provide benefits that will become apparent to the skilled artisan upon reading the following.